This three-year longitudinal study investigated the role of language of instruction in moderating the relationships between initial levels of English oral language proficiency and Spanish reading comprehension and growth in English reading comprehension. The study followed Spanish-speaking English language learners in English-only literacy instruction, an early-exit bilingual program, or a late-exit bilingual program, from third through fifth grade. Students in all groups experienced significant growth in English reading comprehension. For the English-only group, initial levels of Spanish reading comprehension were not related to growth in English reading comprehension. However, for students in the two bilingually instructed groups, those who began with stronger Spanish reading comprehension skills grew faster in English reading comprehension than students without initial strong Spanish reading comprehension skills.